1. Field of the Invention
The present invention relates to a fluid pressure actuated poppet valve, which is opened by a fluid pressure (hereinafter, referred to as an input pressure) supplied from an input port, and which is closed by a fluid pressure (hereinafter, referred to as a pilot pressure) supplied from a pilot port.
2. Description of Related Art
In a case of the fluid pressure actuated poppet valve, in which the valve is driven in a valve opening direction by the input pressure supplied from the input port to an input chamber and is driven in a valve dosing direction by the pilot pressure supplied from the pilot port to a pilot chamber the valve cannot be closed unless the valve closing force is made larger than the valve opening force. Thus, a pressure receiving surface area of the valve on an input pressure side needs to be made smaller than a pressure receiving surface area of the valve on a pilot pressure chamber side. This kind of technique is recited in, for example, U.S. Pat. No. 4,519,572.
FIG. 4A schematically shows the technique of U.S. Pat. No. 4,519,572. A portion of a valve J2, which receives an input pressure from an input chamber J1, is formed as a small diameter portion J3. Another portion of the valve J2, which receives a pilot pressure from a pilot chamber J4, is formed as a large diameter portion J5. A pressure receiving surface area of the valve J2 on an input pressure side is made smaller than a pressure receiving surface area of the valve J2 on a pilot chamber J4 side. In this way, the valve closing force can be made larger than the valve opening force.
However, according to the technique of U.S. Pat. No. 4,519,572, a variable volume portion J6, a volume of which changes in response to movement of the valve J2, is formed in a stepped portion (a portion of varying diameter between the small diameter portion J3 and the large diameter portion J5) of the valve J2.
Therefore, an external drain J7, which communicates the variable volume portion J6 to the outside, needs to be provided to enable a change in the volume of the variable volume portion J6.
Here, in a case where oil is employed as working fluid, the oil is introduced into the variable volume portion J6 through a slide clearance between the small diameter portion J3 and a valve body J8 and a slide clearance between the large diameter portion J5 and the valve body J8. It is thus not possible to use the technique disclosed in U.S. Pat. No. 4,519,572 in a system, which cannot permit oil leakage in a radially outward direction from the valve body J8.
As an alternative, with reference to FIG. 4B, although not recited in U.S. Pat. No. 4,519,572, it is conceivable to provide an O-ring J9 between the small diameter portion J3 and the valve body J8 and another O-ring J10 between the large diameter portion J5 and the valve body J8. In this way, flow of the oil into the variable volume portion J6 can be limited.
However, the provision of the O-rings J9, J10 would degrade the slidability of the valve J2 and thus its response. Furthermore, when the pressure receiving surface area of the valve J2 on the small diameter side and the pressure receiving surface area of the valve J2 on the large diameter side are increased to increase the valve opening force and the valve closing force in order to improve the degraded slidability of the valve J2, which is degraded by the addition of the O-rings J9, J10, the size of the valve J2 is disadvantageously increased. Furthermore, the provision of the O-rings J9, J10 would result in an increase in costs.
In the above case, the oil is used as the example of the working fluid. However, even if the working fluid is changed to another type of liquid or gas, the above disadvantage is still encountered.